ABS resin prepared by graft copolymerization of a rubbery polymer such as diene rubber with an aromatic vinyl compound such as styrene and α-methylstyrene and a cyanated vinyl compound such as acrylonitrile and methacrylonitrile have excellent mechanical strength such as impact resistance and rigidity, moldability, cost performance, and the like, and accordingly, this resin is widely used in applications including home appliance, communications equipment, miscellaneous goods, and medical equipment. Of these applications, high transparency is required in exterior parts applications.
In the case of washing machine application as an example of home appliance, use of ultra-concentrated laundry detergents such as those known in the product names of “NANOX” (registered trademark) and Ultra Attack Neo are recently becoming common. These ultra-concentrated laundry detergents are more likely to deteriorate the resins compared to conventional laundry detergents, and the resin materials used for the washing machine application are required to have a chemical resistance to these chemical reagents. In the meanwhile, the resin materials used for medical equipment application are required to have chemical resistance to rubbing alcohol.
A resin composition is proposed as a resin composition having excellent transparency, chemical resistance, and color tone stability. This resin composition is a thermoplastic resin composition comprising a vinyl copolymer (A) having a graft copolymer (B) dispersed therein, wherein proportion of triplet sequence of the acrylonitrile monomer unit in the acetone-soluble content of the thermoplastic resin composition in relation to the acetone-soluble content is up to 10% by weight (see, for example, Patent Document 1). The transparent ABS resin disclosed in Patent Document 1, however, has been still insufficient for satisfying the recent demands for the high chemical resistance to chemical reagents such as organic solvents, detergents, and solvents such as rubbing alcohol, and the applications are limited.
One means for improving the chemical resistance of the ABS resin known in the art is increasing content of the cyanated vinyl compound. There has been proposed, for example, a thermoplastic resin composition comprising a vinyl copolymer prepared by polymerizing a vinyl monomer mixture containing 10 to 30% by weight of an aromatic vinyl monomer, 50 to 85% by weight of an unsaturated alkyl carboxylate ester monomer, 8 to 15% by weight of a cyanated vinyl monomer having dispersed therein a graft copolymer (B) prepared by graft polymerization of at least one vinyl monomer or vinyl monomer mixture in the presence of a rubbery polymer, and in this thermoplastic resin composition, proportion of triplet sequence of the acrylonitrile monomer unit in the acetone-soluble content of the thermoplastic resin composition in relation to the acetone-soluble content is at least 0.001% by weight and up to 10% by weight (see, for example, Patent Document 2). Also proposed is a transparent thermoplastic resin composition prepared by blending a vinyl copolymer prepared by polymerizing a vinyl monomer mixture containing 10 to 30% by weight of an aromatic vinyl monomer, 30 to 80% by weight of an unsaturated alkyl carboxylate ester monomer, and 1 to 10% by weight of cyanated vinyl monomer, and a graft copolymer prepared by graft polymerization of at least one vinyl monomer in the presence of a rubbery polymer, and this resin composition has a reduced viscosity in methyl ethyl ketone of the acetone-soluble content of the resin composition of 0.70 to 0.75 dl/g (see, for example, Patent Document 3).
As a means for improving impact resistance and flowability of the ABS resin, there has been disclosed, for example, a rubber reinforced thermoplastic resin composition containing a copolymer prepared by copolymerizing a monomer mixture at least containing an aromatic vinyl monomer and a cyanated vinyl monomer, and a graft copolymer prepared by graft polymerization of a monomer mixture at least containing an aromatic vinyl monomer and a cyanated vinyl monomer in the presence of a rubbery polymer, wherein proportion of the components having a molecular weight of less than 50,000 in the acetone-soluble content in relation to the total weight of the acetone-soluble content is less than 30% by weight, and proportion of the components having a molecular weight of at least 250,000 in relation to the total weight of the acetone-soluble content is 5 to 15% by weight, and molecular weight distribution (Mw/Mn) represented by the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the acetone-soluble content is in the range of 1.5 to 2.5 (see, for example, Patent Document 4).